Field of the Invention
The present invention relates to an electric storage cell constituted by an electric storage element sealed with covering film, a covering film, and an electric storage module comprising a stack of such electric storage cells.
Description of the Related Art
Film-sealed batteries, which are electric storage elements sealed with covering film, are widely used in recent years. Film-sealed batteries are subject to rising pressure inside the battery due to generation of gaseous species as a result of electrolysis of the electrolyte medium, if the battery control circuit fails for some reason and abnormal voltage is applied as a result, or if the ambient temperature becomes abnormally high for some reason, while the battery is in use. As their internal pressure rises, film-sealed batteries will eventually experience a rupture of exterior material and gas will erupt from the ruptured area; however, it is not predictable where the rupture may occur, and depending on the location of rupture, surrounding equipment, etc., may be negatively affected.
To solve this problem, a configuration is disclosed in Patent Literature 1, for example, which involves a covering film whose seal part has a peninsula-shaped projected fusing part, so that when the covering film package expands and the projected fusing part peels, a through hole will be formed to serve as a pressure release part. This way, the peel-off stress generated by expansion of the film can be concentrated onto the projected fusing part to facilitate the progress of its peeling, thereby facilitating the release of the pressure caused by expansion of the package.